1. Mountains, climate, and carbon
26 Jan 2015
Cin-Ty Lee

2. Temperature of the Earth
Climate
Temperature of the Earth
Solar insolation
Albedo
Absorption
greenhouse gas

3. What controls climate on 10-100 My timescales?
ΔT (oC) +2 +4 +6 -2 -4 K J Tr P C D S O
100
200
300
400
500
Veizer et al. 2000
Prepared by Rohde
Solar insolation
Albedo
Absorption
greenhouse gas
e.g., CO2

4. Cretaceous-Paleogene -Warm -pCO2 was >4-8 x higher than today
Mid- to late Cenozoic
-Cooling
-Low pCO2
Zachos et al. 2001

5. -- what role do mountains play in climate? Whole Earth carbon cycling
Global Carbon Cycle
CaCO3 + SiO2 = CaSiO3 + CO2
Metamorphism, volcanism
Silicate weathering, carbonate deposition
Dasgupta and Hirschmann, 2010

6. What controls pCO2 in atmosphere?
dCO2/dt = input – output
If response time of ocean atmosphere is 100 ky, then on My timescales, we can assume steady state
Output = k pCO2n
pCO2 ~ (Input/k)1/n

7. How do you change the pCO2 state of the Earth?

8. dCO2/dt = input – output Output = k pCO2n pCO2 ~ (Input/k)1/n
If response time of ocean atmosphere is 100 ky, then on My timescales, we can assume steady state
Volcanoes, metamorphism, carbonate weathering
Input
pCO2
Output = k pCO2n
pCO2 ~ (Input/k)1/n
output
Precipitation of carbonate
Inspired by Kazumi Ozaki

9. Increase outputs, pCO2 decreases
Increase weathering rates and carbonate deposition rates?
Input
pCO2
output

10. dCO2/dt = input – output
If response time of ocean atmosphere is 100 ky, then on My timescales, we can assume steady state
Input
pCO2
Output = k pCO2n
output
Inspired by Kazumi Ozaki

11. Increase inputs, pCO2 increases
pCO2
output
Inspired by Kazumi Ozaki

12. Are long-term climatic oscillations “driven” by endogenic forcings (INPUTS)?
Or are they “driven” by the nature of the weathering response (OUTPUTS)?

13. CO2 Continental Arc Island arc Magma/lava/ash Oceanic crust
Sediment or carbonated crust

14. Global Carbon Cycle CaCO3 + SiO2 = CaSiO3 + CO2
Metamorphism, volcanism
Silicate weathering, carbonate deposition
Note: there’s also an organic C cycle component, but for simplicity, let’s ignore that for now
Ridgwell and Zeebe, 2005

15. What types of mountain building processes produce the most CO2?
How are these events/processes related to regional or global mantle dynamics?

16. An input-driven world?
Did Cretaceous continental arcs intersect carbonates globally and force greenhouse conditions?
Pre-Cretaceous carbonate distribution
SNB
SNB
PRB
PRB A B
Lee et al., 2013; Geosphere

17. Zachos et al. 2001

18. Raymo and Ruddiman, 1992

20. Mountains can influence climate in other ways
hydrologic cycle  chemical weathering  CO2 drawdown  temperature decrease

21. Journal of Climate, 2014

22. Molnar, Boos, Battisti 2010

23. Molnar, Boos, Battisti 2010

24. Or are we a sink-driven world….
Where the rise of mountains, enhances chemical weathering rates and burial of carbonate and organic C
Did mountain building “drive” Cenozoic cooling?

25. Correlation does not equal causation

28. Surface uplift = rock uplift - exhumation
Surface uplift = change in average surface elevation
Rock uplift = change in elevation of uneroded rock
= paleo-altimetry
Exhumation = amount of overburden removed
= metamorphic pressure

30. Paleo-altimetry represents rock uplift, not average surface elevation
Could enhanced alpine glaciation, after the onset of northern hemisphere glaciation 3 Ma have caused rock uplift, masquerading as tectonics?
Raymo and Huybers

31. How do we tease apart surface and rock uplift and exhumation?

32. What controls average surface elevation?
Rocky Mtns, USA
Andes
Tibet
other
Elevation h (km)
Thickness (km)

33. cgH = mg(H-h) h = (/m)H Isostasy
continents ride on “fluid” substrate
timescales for isostatic equilibrium is > Maxwell time (10,000 yrs)
h = elevation
cgH = mg(H-h) rc H rm
h = (/m)H

34. Free-air gravity anomaly
Commission de la carte geologique du monde (CCGM)
Continents and oceans have near-zero free-air gravity anomalies. This means continents and oceans are in isostatic equilibrium.
Even high mountain ranges like Tibet, Andes, and Cordillera are not significantly out of isostatic equilibrium.
Isostatic anomalies exist on Greenland and Hudson bay and on short wavelengths due to elastic flexure on plates

35. Isostatic equilibrium does not mean that mountains or continents are gravitationally stable
Thickened crustal columns in isostatic equilibrium can still collapse or delaminate!
Zhang et al. 2004

36. Scatter could be related to dynamic effects or mantle buoyancyh r rc rm hb
Htotal
Elevations of mountains primarily controlled by crustal thickness, NOT by dynamic effects or mantle buoyancy
Scatter could be related to dynamic effects or mantle buoyancy
Cratons - mysterious
Rocky Mtns, USA
Andes
Tibet
other
2.6
2.7
2.8
2.9
3.0
rm = 3.33 g/cm3
Elevation h (km) rc
3.1 g/cm3
cratons
Thickness (km)

37. What controls crustal thickness
tectonics E
erosion rc rm
foundering M
magmatism
foundering &
Subduction erosion

38. And what is the effect on Carbon Cycling?rc rm
foundering M

40. What does the U/Pb age in zircon histogram mean?
Episodic crust formation?
Episodic mountain building?
Biases in the composition of crust being formed?
Episodic plate tectonics?
What is the link with continents?
Condie and Aster, 2010